Onion Thrips (Thrips tabaci) is a pest that infects a variety of plants, causing the most economic damage to onions, leeks and garlics.

Researchers have developed the Onion Thrips growing degree day model, available on the Pest Prophet app, in order to help predict when different life stage events will occur, based on the weather.

Calculating Growing Degree Day Units

The Onion Thrips growing degree day model uses a lower threshold of 11.5C  for calculating growing degree day units. The growing degree day units can be calculated from daily maximum and minimum temperatures using these thresholds, or by using the Pest Prophet app, which features this model and is easy to set up and use.

Setting the Biofix date

In order to begin growing degree day accumulation, first a “biofix” date must be set which is the first date, after which growing degree day units will begin to accumulate. In the Pest Prophet app, the biofix date can be adjusted for any observed life cycle stages.

For the Onion Thrips model, in order to predict the emergence of second generation thrips, the biofix date should be set when adult thrips are first observed and eggs are laid. Larvae will first be observed 78 GDD (C) after the biofix date, with adults emerging 100 GDD (C) after that.

For best results the biofix should be re-adjusted for each generation, based on scouting observations. This will improve accuracy of later crop stage predictions.

Sources:

Edelson, J. V., and J. J. Magaro. 1988. Development of onion thrips, Thrips tabaci Lindeman, as a function of temperature. SW Entomol. 13: 171-176.